Provides interfaces that need to be implemented by web browser adapters.
Package Specification
Base Help System, requires web browser to display help document.  Since
availability of web browsers differ from system to system, it is possible
to configure browser adapters in addition to ones provided with the base. 
The browser (or browser adapter) can be configured by
providing extension for org.eclipse.help.base.browser extension point. 
If more than one browser is available on a user system, the default browser
can be designated in Help preference page.
In general terms, implementing a web browser involves:
- 
Implementing standalone UI element having the IBrowserAPI, and
capable of displaying HTML documents given a URL.
- 
Providing a factory for managing of browsers on a particular system, by
implementing IBrowserFactoryinterface.
- 
Declaring an extension of the org.eclipse.help.base.browserextension
point that mentions the name of that factory class.
Note that browser factory will be created on every system.  If the
factory is not capable of creating a browser on some system configurations,
due to missing prerequisites e.t.c., itsisAvailable() method
should be returning false on these systems.